2010年职称英语理工类C级阅读理解考点精华(3)

        Plant Gas
　　Scientists have been studying natural sources of methane for decades but hadn’t regarded plants as a producer，notes Frank Keppler，a geochem[st at the Max Planck Institute for Nuclear Physics in Heidelberg，Germany1.Now Keppler and his colleagues find that plants，from grasses to trees，may also be sources of the greenhouse gas.This is really surprising，because most scientists assumed that methane production requires an oxygen-free environment.
　　Previously，researchers had thought that it was impossible for plants to make significant amounts of the gas.They had assumed that，microbes2 need to be in environments without oxygen to produce methane.Methane is a greenhouse gas，like carbon dioxide.Gases such as methane and carbon dioxide trap heat in Earth’s atmosphere and contributeto global warming.
　　In its experiments，Keppler’s team used sealed chambers that contained the same concentration of oxygen that Earth’s atmosphere has.They measured the amounts of methane that were released by both living plants;and dried plant material，such as fallen leaves.